WASHINGTON (Reuters) - A U.S. Agriculture Department laboratory will conduct further tests on an animal suspected of having mad cow disease before sending samples to Britain to confirm the results, a spokesman said on Saturday.

The USDA reported late on Friday an older animal tested positive for the brain-wasting disease, reigniting fears that foreign countries would shun U.S. beef again.

The government said the suspect animal, which was first tested back in November, did not enter the human food or livestock feed supply.

The only confirmed U.S. case of bovine spongiform encephalopathy, or mad cow disease, was found in December 2003 in a Washington state dairy cow. The discovery halted billions of dollars worth of American beef exports.

Agriculture department Ed Loyd said the department's laboratory in Ames, Iowa, would conduct a couple more tests before sending brain samples to Weybridge in Great Britain next week.

"We are running it through again to ensure the results," Loyd said. "We want to also ensure we send samples to Weybridge that are adequate enough for them to conduct appropriate testing that allows for a valid result."

Loyd said it was unclear whether the agriculture department would announce the follow-up test results from Ames. "I was told we wouldn't have anything else this weekend."

The USDA said it did not believe the incident would have an impact on the U.S. beef trade.

Washington has informed all of its agriculture attaches overseas about the suspect animal. "Certainly an important part of what we do over the next few days will be to keep all of our trading partners informed of our progress," Loyd said.

USDA officials have been pressing for resumed purchases of American beef by Japan and South Korea, which both were major buyers until they suspended purchases in December 2003.

The USDA said the suspect animal tested positive for BSE in a rapid, preliminary test in November. When retested with more sophisticated technology, it was found free of the disease.

But the agriculture department's inspector general asked department scientists this week to retest the suspect animal, using a third kind of technology known as the "Western blot" test. The animal tested positive late on Friday.